This application relates to measurements of electromagnetic properties and interactions of various materials, and more specifically, to techniques and systems for measuring electromagnetic properties and interactions based on radiation-excited polarizations.
Various materials respond to an external radiation field, e.g., an electromagnetic irradiation, to develop electromagnetic polarization. The interaction between the induced polarization in a material and the radiation field can be measured or monitored to provide useful information for a variety of applications including, among others, imaging, spectroscopy, recording, and determination of distances and angles. Non-destructive measurements based on such interaction of high spatial resolution and detection sensitivity are particularly desirable. A number of techniques have been developed to meet such needs. Examples include the scanning tunneling microscope, atomic force microscope, and near-field scanning optical microscope.
Many of such techniques operate based on detection of electromagnetic emission from a sample under excitation of an external field. In incoherent spontaneous emission, the signal to be detected is essentially determined by the multiplication of the average excited state population and the rate of emission. In methods based on coherent emission, it is useful to describe the detection as being of those field modes into which the sample has radiated. In both cases, the detection sensitivity is generally limited by the quantum limit of the “shot noise” that is inherent in the detection.